This invention relates generally to a method for preparing organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals. More specifically the method involves the reaction of an aminoalkylsilane or siloxane with acyl halides in the presence of a large particle size, solid base.
Organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals are well known and have been described in U.S. Pat. No. 4,608,270 to Varaprath, which is herein incorporated by reference.
As mentioned in Varaprath U.S. Pat. Nos. 4,608,270 and as taught in 2,929,829 to Morehouse, Japan 51/108022 to Furuya et al., Japan 56/74113 to Takamizawa, and West German DE 2365272 to Koetzsch et al., acyl-amino-organo-poly siloxanes can be synthesized by reacting aminosiloxanes with the corresponding acid chloride in the presence of a tertiary amine such as triethylamine. However such a synthesis has several disadvantages. First, the removal of the voluminous precipitate of triethylamine hydrochloride by filtration is tedious. Second, a small amount of HCl is liberated even when an excess of amine is used. This HCl is detrimental to the stability of the polymer, especially when the acid chloride has a reactive vinyl functionality such as where the acid chloride is methacrylyl chloride.
An alternative method for the preparation of acyl-amino-organo-poly-siloxanes involves the reaction of aminosiloxanes and silanes with an acid anhydride or ester at elevated temperature. This is taught in U.S. Pat. No. 4,507,455 to Tangney and Ziemelis, assigned to the assignee of the present invention. Unfortunately at the elevated temperatures of the reaction, acrylamide derivatives undergo Michael addition and amidation of the acrylic double bond resulting in unwanted byproducts and crosslinkage of the desired product which ultimately causes the polymer to gel.
Finally as taught in the above-mentioned U.S. Pat. No. 4,608,270 to Varaprath, these problems can be overcome by reacting the aminosilanes and siloxanes with acid chlorides in the presence of an aqueous base such as sodium hydroxide. The HCl that is produced on addition of acyl chloride is neutralized by the hydroxide in the aqueous phase. However, several problems arise from the fact that this reaction is carried out in a two-phase aqueous system in which the aminosiloxane is dissolved in an organic solvent that is immiscible with water. First, the presence of water makes it very difficult to prepare compounds with moisture sensitive functionalities such as methoxy. Second, the presence of metal ions from the base can create a contamination problems. Third, the aqueous base can react with the siloxane bonds in an unwanted manner. Finally, because the amide function is generally highly polar and hydrophilic, it has a tendency to absorb moisture. Incorporation of these units into the siloxane backbone increases water miscibility causing the polymers to emulsify easily thus making phase separation difficult.
To some extent, the latter problem can be overcome by using chlorinated solvents such as methylene chloride or chloroform but, unfortunately, such solvents are environmentally undesirable. Moreover, when larger amounts of amide functionality or more resinous structure or both are used, it is almost impossible to prepare such compounds using a two-phase system even when chlorinated solvents are used.
Accordingly, the need remains for an improved and easier method for preparing acylamino organosilicon compounds that avoids phase separation, base metal ion contamination, filtration, unwanted siloxane bond reactivity, and the solvent toxicity problems previously encountered. The need also remains for an expanded method that permits use of aminosilicon starting materials having hydrolytically unstable groups such as SiOCH.sub.3.